<!--
 * @Author: WangGuojian 1085844536@qq.com
 * @Date: 2023-08-05 16:29:55
 * @LastEditTime: 2023-08-05 16:53:40
 * @LastEditors: WangGuojian 1085844536@qq.com
 * @FilePath: \vue-basic\09-监视属性\2.天气案例_监视属性.html
 * @Description:
-->
<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title>天气案例_监视属性</title>
        <script type="text/javascript" src="../js/vue.js"></script>
    </head>
    <body>
        <!--
            监视属性watch
                1.当被监视的属性变化时，回调函数自动调用，进行相关操作
                2.监视的属性必须存在，才能进行监视
                3.监视的两种写法：
                    (1).new Vue 时传入watch配置
                    (2).通过vm.$watch监视
         -->
        <!-- 准备一个容器 -->
        <div id="root">
            <h2>今天天气很{{info}}</h2>
            <button @click="changeWeather">切换天气</button>
        </div>
    </body>
    <script type="text/javascript">
        Vue.config.productionTip = false;

        const vm = new Vue({
            el: '#root',
            data: {
                isHot: true,
            },
            computed: {
                info() {
                    return this.isHot ? '炎热' : '凉爽';
                },
            },
            methods: {
                changeWeather() {
                    this.isHot = !this.isHot;
                },
            },
            // watch: {
            //     isHot: {
            //         immediate: true, // 初始化时让handler调用一下
            //         // handler什么时候调用？当isHot发生改变时
            //         handler(newValue, oldValue) {
            //             console.log('isHot被修改了', newValue, oldValue);
            //         },
            //     },
            // },
        });

        vm.$watch('isHot', {
            immediate: true,
            handler(newValue, oldValue) {
                console.log('isHot被修改了', newValue, oldValue);
            },
        });
    </script>
</html>
